This invention relates to an apparatus and method for removing an image from the ribbon of a thermal transfer printer after the printing process has taken place. In particular, the method involves the use of a heated roller which is applied to the ribbon in order to liquify the wax based ink remaining on the ribbon so as to obliterate the image previously left thereon.
It is generally known that thermal transfer printing mechanisms include a disposable printing ribbon in contact with a thermal printhead in order to cause the transfer of ink coated along the ribbon to a receptor surface, which is usually a sheet of paper. The printhead typically contains minute resistors arranged in a row and positioned so that they come into contact with the ribbon along a line which is substantially perpendicular to the direction of movement of the ribbon during operation of the printing mechanism. When an electrical current is passed through the resistors, the heat generated therefrom causes the ink coated along the ribbon to be transferred to the sheet of paper. In order to create the desired printout, the number and location of dots to be printed in each row, and the longitudinal incrementing of ribbon movement perpendicular to the array of resistors on the printhead, as well as the longitudinal incrementing of paper movement, are properly selected, usually under microprocessor control.
However, conventional thermal transfer printing mechanisms are not completely satisfactory. Because a negative image of the printed character is left on the printing ribbon after transfer of the ink to the paper, it is possible to read the printed message by examining the ribbon after use in the printer. It is known that thermal transfer printers are commonly used to print airline tickets, credit card transaction receipts, etc., the content of which may include credit card numbers, fares and other proprietary or sensitive information. Therefore, if disposal of the spent thermal transfer ribbon is not adequately achieved, unauthorized persons may be able to reconstruct that information by merely examining the spent ribbon. Consequently, the secrecy of that information cannot be maintained unless additional security measures are employed (security guards, hidden cameras, etc.), necessitating further expenses.
Accordingly, it is desirable to provide a printing mechanism in which the images left on the ribbon during the printing operation are removed or obliterated.